Volcanic plumbing filters on ocean-island basalt geochemistry

Ocean-island basalts (OIBs) are considered to be messengers from the deep mantle, yet the filtering effect of the plumbing systems that bring OIB melts to the surface remains poorly assessed. We investigated volcanic products from El Hierro island (Canary Islands) from textural and chemical perspectives. The majority of geochemical data cluster at relatively fractionated basaltic compositions of 5 wt% MgO. Compositions ≥10 wt% MgO are porphyritic whole rocks that accumulate mafic minerals. Near-primary melts do not erupt. Instead, we show that carrier melts (crystal-free whole rocks, glasses, and melt inclusions) are consistently buffered to low-MgO compositions during passage through the plumbing system. We tested our model of melt fractionation and crystal accumulation on a global compilation of OIBs. Similar to El Hierro, the majority of data cluster at evolved compositions of 5 wt% MgO (alkaline) to 7 wt% MgO (tholeiitic). Modeling the fractionation of OIB parental melts, we show that with 50% crystallization, OIB melts reach 5 wt% MgO with reduced density, increased volatile content, and overall low viscosity, becoming positively buoyant relative to wall rocks and highly eruptible when reaching volatile saturation at depths around the crust-mantle boundary. Under these conditions, 5 wt% MgO OIB “sweet spot” melts are propelled to the surface and erupt carrying an assortment of recycled crystals. This mechanism is consistent with the petrography and chemistry of erupted products and suggests OIB volcanoes are dominated by low-MgO basaltic melts.

Exploring the links between volcano flank collapse and the magmatic evolution of an ocean island volcano: Fogo, Cape Verde

Mass-wasting of ocean island volcanoes is a well-documented phenomenon. Massive flank collapses may imply tens to hundreds of km3 and generate mega-tsunamis. However, the causal links between this large-scale, low-frequency instability, and the time–space evolution of magma storage, crystal fractionation/accumulation, lithospheric assimilation, and partial melting remains unclear. This paper aims at tracking time variations and links between lithospheric, crustal and surface processes before and after a major flank collapse (Monte Amarelo collapse ca. 70 ka) of Fogo volcano, Cape Verde Islands, by analysing the chemical composition (major, trace elements, and Sr–Nd–Pb isotopes) and age-controlled stratigraphy (K–Ar and Ar–Ar dating) of lavas along vertical sections (Bordeira caldera walls). The high-resolution sampling allows detecting original variations of composition at different time-scales: (1) a 60 kyrs-long period of increase of magma differentiation before the collapse; (2) a 10 kyrs-long episode of reorganization of magma storage and evacuation of residual magmas (enriched in incompatible elements) after the collapse; and (3) a delayed impact at the lithospheric scale ~ 50 kyrs after the collapse (increasing EM1-like materiel assimilation).

Oxidized Mantle Sources of HIMU and EM-type Ocean Island Basalts

Oxygen fugacity (fO2) is a fundamental variable in igneous petrology with utility as a potential tracer of recycled surficial materials in the sources of mantle-derived lavas. It has been postulated that ocean island basalts (OIB) have elevated fO2 relative to mid-ocean ridge basalts (MORB) owing to more oxidized source regions. To clarify this issue, trace-element systematics of olivine grains are reported from OIB lavas with HIMU (high-; Mangaia, Canary Islands), enriched mantle (EM; Samoa; São Miguel, Azores Islands) and depleted MORB mantle (DMM; Pico, Azores) Sr-Nd-Pb-Os isotopic signatures, to constrain the fO2 of each magmatic system. Despite sampling distinct mantle reservoirs based on radiogenic isotope systematics, these OIB suites show similar fO2, ranging from +1.5 to +2.9 FMQ, with an average of 2.0 ± 0.7 FMQ, significantly higher than MORB at +0.6 ± 0.2 FMQ using the same oxybarometer. OIBs show no correlation between fO2 and bulk rock isotopic ratios or parental magma compositions. The lack of correlations with isotopic signatures likely results from radiogenic isotope signatures being hosted in volumetrically minor trace element enriched mantle lithologies, while fO2 reflects the volumetrically dominant mantle component. Higher fO2 in OIB relative to MORB implies a uniformly oxidizing plume source mantle that may be the result of either a common oxidized oceanic crust-rich reservoir parental to all modern plume lavas, or preservation of un-degassed and oxidized mantle domains formed early in Earth history.

epidemiology of injury and illness amongst athletes at the Indian Ocean Island Games, Mauritius 2019

Background: The Indian Ocean Island Games is a multi-sport event that occurs every four years and includes athletes from seven islands of the Indian Ocean. Objective: This study aims to describe the injury and illness epidemiology of the athletes participating during the 2019 Indian Ocean Islands Games. Material and Methods: This prospective cohort study recorded injury and illness cases from athletes who competed in these Games. All medical physicians received detailed instructions and training on data collection using an injury report form. All athletes (minor and adults) who provided consent, or consent given from the minors’ guardians, were included in this study. Athletes who did not provide consent for this study were excluded. Results: 1 521 athletes (531 women and 990 men) reported 12 injuries per 100 athletes (n=160) and 6 illnesses per 100 athletes (n=85). The percentage of distribution of injuries were highest in football and basketball. Most injuries occurred during competition compared with training Joint sprains were the most common type of injury (28%), followed by muscle strains (19%). Men suffered the majority of injuries (79% vs. 21%). Similarly, men sustained more illness than women (57% vs. 43%). Most illnesses affected the respiratory system (67%), and infection was the most common cause of illness (84%) in participating athletes. Discussion: These findings are similar to previous events in other parts of the world. However, unique ailments, not previously reported on, were discovered. Conclusion: Epidemiological data from this study can be inferred to athletes who compete in similar multi-sport events and/or Olympic Games in the Indian Ocean region.

Supplemental Material: Volcanic plumbing filters on ocean-island basalt geochemistry

Data (Tables S1–S8), methods, and Figures S1–S3.<br>

Supplemental Material: Volcanic plumbing filters on ocean-island basalt geochemistry

Data (Tables S1–S8), methods, and Figures S1–S3.<br>